L Recent advances in tissue engineering have made possible the creation of a xenogeneic bioartificial liver (BAL) as part of an effort to improve the survival of patients with acute liver failure (ALF). A major obstacle that faces this and most other tissue-engineered cell based products is the problem of storage. Potentially, hypothermic conditions may be utilized to allow the viable storage of the BAL from point of production to delivery. Indeed previous experiments using the BAL have shown that up to a 24-hour period of cold storage is feasible. However, longer storage time as well as improved viability and function is vital for its successful widespread application. Examination of the cellular mechanisms, specifically the gene expression patterns associated with the early phases of hypothermic damage, need to be examined in order to discover and subsequently test "protective" factors. New techniques in tissue culture and molecular/cellular biology make this goal attainable. We propose that exposure to hypothermia will cause an up-regulation in the expression of common motifs present in the cluster of co-regulated genes dealing with apoptosis and stress; furthermore, that these expression patterns are modified in the presence of "protective" factors. Our specific aims include establishment of gene expression patterns in cold-exposed mouse hepatocytes using microarray technology as well as suppression subtractive hybridization, studying modification of such patterns in the presence of a protective factor (sublethal pre-stress heat exposure), and finally, determination of the ideal cold-storage conditions in an "optimized" micro-BAL. We hope that our findings will facilitate prolongation of the cold storage period and improve the viability and function of the BAL. Even though the immediate benefit of this proposal will be for the BAL, we strongly believe that it will have significant implications for most xenogeneic-based, tissue-engineered artificial organs.